Determination of key quality parameters of palm oil, such as the iodine value (IV), are typically performed using time consuming and costly wet chemical methods.

This application note demonstrates that the Metrohm DS2500 Liquid Analyzer operating in the visible and near infrared spectral region (Vis-NIR) provides a cost-efficient and fast solution for the determination of these quality control parameters in palm oil. With no sample preparation or chemicals needed, Vis-NIR spectroscopy allows for the analysis of palm oil in less than a minute and can be used by anyone.

DS2500 Liquid Analyzer and a palm oil sample present in an 8 mm disposable vial.
Figure 1. DS2500 Liquid Analyzer and a palm oil sample present in an 8 mm disposable vial.

Palm oil samples which have been refined, bleached, and deodorized (RBD palm oil) were measured in transmission mode with a DS2500 Liquid Analyzer over the full wavelength range (400–2500 nm). The highly viscous samples were liquefied using the Vial Heater. Reproducible spectrum acquisition was achieved using the built-in temperature control (at 60 °C) of the DS2500 Liquid Analyzer. For convenience, disposable vials with a path length of 8 mm were used, which made cleaning of the sample vessels unnecessary. The Metrohm software package Vision Air Complete was used for all data acquisition and prediction model development. The measurements were also conducted with a XDS RapidLiquid Analyzer to compare the analytical performance of both instruments.

Table 1. Hardware and software equipment overview
Equipment Metrohm number
DS2500 Liquid Analyzer 2.929.0010
XDS RapidLiquid Analyzer 2.921.1410
Vial Heater 2.921.9010
Disposable vials, 8 mm diameter, transmission 6.7402.000
Vision Air 2.0 Complete 6.6072.208

The obtained Vis-NIR spectra (Figure 2) were used to create prediction models for quantification of the individual key parameters. The quality of the prediction models was evaluated using correlation diagrams, which display the correlation between VisNIR prediction and primary method values. The respective figures of merit (FOM) display the expected precision of a prediction during routine analysis.

Figure 2. Vis-NIR spectra of palm oil obtained using a DS2500 Liquid Analyzer / XDS RLA and 8 mm disposable vials.
Figure 3. Correlation diagram for the prediction of the iodine value (IV) in palm oil using a DS2500 Liquid Analyzer. The iodine lab value was evaluated using titration.
Table 2. Figures of merit for the prediction of the iodine value (IV) in palm oil using a DS2500 Liquid Analyzer.
Figures of merit Value
R2 0.998
Standard error of calibration 0.49 g/100g
Standard error of cross-validation 0.49 g/100g
Figure 4. Correlation diagram for the prediction of the iodine value (IV) in palm oil using a XDS RapidLiquid Analyzer. The iodine lab value was evaluated using titration.
Table 2. Figures of merit for the prediction of the iodine value (IV) in palm oil using a XDS RapidLiquid Analyzer.
Figures of merit Value
R2 0.998
Standard error of calibration 0.55 g/100g
Standard error of cross-validation 0.54 g/100g

This application note demonstrates the feasibility of the DS2500 Liquid Analyzer for the analysis of the iodine value in palm oil. Compared to the older generation XDS RLA, the observed accuracy is slightly better, yet within statistical relevance.

In a previous application note (AN-NIR-044), the XDS RLA was used to determine additional quality parameters in palm oil, including free fatty acids, moisture content, and the deterioration of bleachability index (DOBI). Due to the demonstrated comparability between the DS2500 Liquid Analyzer and XDS RapidLiquid Analyzer, it is clear that those parameters can also be determined with the DS2500 Liquid Analyzer.

The main advantages of NIR spectroscopy over wet chemical methods are that, running costs are significantly lower and time-to-result is significantly reduced.

AN-NIR-044 - Quality Control of Palm Oil – Environmentally friendly determination of FFA content, iodine value, moisture, DOBI, and carotene content

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